Telescopic Conductor Casing for a Well Installation and a Method of Driving Same into the Underground

ABSTRACT

A conductor casing device for establishing and lining a wellbore in unconsolidated sediments, the conductor casing being arranged to be driven into and to displace the unconsolidated sediments by axially directed impulses against an internal abutment in the lower portion of the conductor casing, where the conductor casing is telescopic. The invention also comprises a method of driving a telescopic conductor casing into unconsolidated sediments.

The invention regards a telescopic conductor casing for a well installation, preferably a sub sea hydrocarbon well, more particularly a telescopic conductor casing in which an outer pipe is releasably coupled to an inner pipe, the lower end of which comprises means of cooperating with a driving mechanism. When the conductor casing has been driven far enough into the unconsolidated sediments so as to project a prescribed distance above the surface of the unconsolidated sediments, the outer pipe is separated from the inner pipe. The inner pipe is driven further into the unconsolidated sediments until it encounters solid sediments or reaches the planned driving depth. A device by the lower end of the outer pipe ensures that the outer pipe cannot be pushed down on the outside the inner pipe. The invention also comprises a method of driving a telescopic conductor casing into the ground.

When establishing a well such as a hydrocarbon well in an area with unconsolidated sediments above the rock structures, it is necessary to insert a conductor casing through the unconsolidated sediments. The conductor casing separates the wellbore from the unconsolidated sediments and acts as a foundation for installations (wellhead, BOP etc.) at the surface of the unconsolidated sediments. The installations will, in accordance with regulations, be placed at a certain height relative to the surface, i.e. ground surface or seabed. Analyses of the unconsolidated sediments form the basis for the selection of a conductor casing length, which in all probability can be driven far enough down for the upper end of the conductor casing to attain a prescribed height above the unconsolidated sediments. When there is uncertainty with regards to the condition of the unconsolidated sediments, the length of the conductor casing may be to great or too small, and it becomes necessary, particularly when establishing a sub sea well, to carry out complicated operations to lengthen or shorten the conductor casing so as to achieve the correct height for the upper end of the casing.

The object of the invention is to remedy the disadvantages of prior art. In particular, the object is to reduce the cost and practical effects of the uncertainty involved in estimating how far the conductor casing can be driven.

The invention also allows the installation of long conductor casings without requiring additional conductor casing sections to be added during the driving.

The object is achieved by the characteristics given in the description below and in the following claims.

A telescopic conductor casing according to the invention is arranged in a known manner to be driven into unconsolidated sediments by means of axially directed impulses against internally placed impact surfaces, preferably in the lower portion of an inner pipe. The inner pipe is removably coupled to an outer pipe, preferably by an upper portion of the inner pipe being coupled to an upper portion of the outer pipe.

In the lower portion of the outer pipe there is provided, in a non-displaceable manner, one or more locking members abutting the outside wall of the inner pipe. The locking element(s) is/are arranged to allow an inner pipe released from the outer pipe to move axially away from the upper portion of the outer pipe. The locking element(s) is/are furthermore arranged to prevent an outer pipe released from the inner pipe to move axially towards the lower portion of the inner pipe.

Preferably, the outer pipe is arranged to receive one or more known stabilizers located externally. This is particularly relevant when the conductor casing is to be placed in unstable unconsolidated sediments. The stabilizers causes the conductor casing to present a greater abutment surface to the unconsolidated sediments, whereby the unconsolidated sediments can accommodate a greater load directed radially of the pipe.

Preferably, the outer pipe is provided with one or more stops arranged to abut an upper portion of the stabilizer(s). This makes it possible to place the stabilizer(s) at a predefined level relative to the surface of the unconsolidated sediments when they are driven into the unconsolidated sediments along with the outer pipe.

The invention further comprises a method of driving a conductor casing into unconsolidated sediments in order to line a wellbore, the conductor casing being arranged to be driven into the unconsolidated sediments by axially directed impulses against an internal abutment in the lower portion of the conductor casing, where:

-   -   an outer pipe is removably coupled to the upper portion of an         inner pipe;     -   the compound telescopic conductor casing is driven into the         unconsolidated sediments until the upper portion of the outer         pipe assumes a prescribed distance from the surface of the         unconsolidated sediments;     -   the outer pipe is released from the inner pipe;     -   the inner pipe is driven further into the unconsolidated         sediments until it reaches the planned driving depth or until no         further driving is possible, the inner pipe moving away from the         upper portion of the outer pipe in the axial direction.

Preferably, the method comprises the provision of one or more stabilizers on the outer pipe prior to driving this into the unconsolidated sediments.

The following describes a non-limiting example of a preferred embodiment illustrated in the accompanying drawings, in which:

FIG. 1 shows a longitudinal section through an assembled telescopic conductor casing according to the invention;

FIG. 2 shows a longitudinal section, on a smaller scale, through an assembled telescopic conductor casing being driven into unconsolidated sediments;

FIG. 3 shows a longitudinal section through the telescopic conductor casing being driven into unconsolidated sediments, with an inner pipe sliding in a disconnected outer pipe;

FIG. 4 shows a side view of a conductor casing corresponding to the longitudinal section of FIG. 3, but where the outer pipe is provided with a stabilizer; and

FIG. 5 shows a top view of the conductor casing in FIG. 4.

Reference is first made FIG. 1, in which a telescopic conductor casing 1 comprises an inner pipe 3, an outer pipe 5, an annular coupling device 7 and also an annular locking member 9.

The upper portion 11 of the inner pipe 3 is provided with an annular coupling groove 13. A lower portion 15 of the inner pipe 3 is provided with a driving shoe 17 with an internal striking surface 19.

An upper portion 21 of the outer pipe 5 is provided with an external coupling section 23 capable of receiving and retaining a well installation (not shown). The outside of a central portion 25 of the outer pipe has annular stabilizing stops 27. A lower portion 28 of the outer pipe is provided with an internal annular locking groove 29.

The coupling device 7 has an internal coupling section 31 that extends from a lower central opening 33. The threaded portion 31 of the coupling device 7 is a complementary fit to the coupling section 23 on the outer pipe 5. An upper bore 35 is a complementary fit to the outer diameter of the inner pipe 3. An annular shoulder 37 is a complementary fit to the coupling groove 13 on the inner pipe 3. The coupling device is removable, being divisible (not shown) by means of a tool-bearing remote operated vehicle (not shown).

The locking element 9 is shaped like an annular disk spring with a convex ring surface 41 facing the lower end 15 of the outer pipe 5. An internal lip 43 tightly abuts the outer wall of the inner pipe 3.

Reference is now made essentially to FIGS. 2 and 3. The conductor casing 1 has been driven into unconsolidated sediments 51 by means of an internally placed hammer 61, 63 connected to a driving and control mechanism (not shown) via a cable 65. The hammer 61, 63 can transmit driving impulses to the conductor casing via the impact surface 19.

In an alternative embodiment the conductor casing 1 is provided with a cylindrical stabilizer 71 enclosing portions of the outer pipe 5. A central pipe 73 encloses the outer pipe 5 coaxially and abuts the stabilizer stop 27 when in the active position. A cylindrical jacket 77 is coaxial with the central pipe 73 and is rigidly connected to this by several supporting ribs 75 that project in the radial direction from the central pipe 73 and extend along the entire axial length of the stabilizer 71.

Prior to driving a conductor casing 1 into the ground, the unconsolidated sediments 51 are analysed to find out how far the conductor casing 1 can be driven and how much uncertainty exists around this analysis, i.e. what is the expected maximum driving depth and what is the estimated minimum driving depth. Then a length of inner pipe 3 is selected which under no circumstances will cause the inner pipe 3 to protrude above the unconsolidated sediments by more than what is prescribed for a well installation which is subsequently to be installed on the conductor casing 1. Also, the length of the outer pipe 5 is selected to be such that the outer pipe 5, when protruding above the unconsolidated sediments 51 as prescribed with regard to the well installation, overlaps the inner pipe when this has been driven down to the maximum depth.

The conductor casing 1 is driven into the unconsolidated sediments 51 in a manner that is known per se, by the hammer 61, 63 partly making a hole by penetrating into the unconsolidated sediments 51 and forcing them aside and partly hammering the conductor casing into the unconsolidated sediments 51 through impacts against the impact surface 19 on the driving shoe 17. During the first part of the driving, the coupling device 7 interconnects the inner and outer pipes 3, 5 of the conductor casing 1.

When the outer pipe 5 has reached a prescribed depth, i.e. it protrudes above the unconsolidated sediments 51 at a prescribed height, the coupling device 7 is removed; at a sub sea installation preferably through use of tools on a remote operated vehicle (ROV).

The driving then continues, the inner pipe 3 moving axially through the outer pipe 5 by sliding through the locking member 9. When the inner pipe 3 has reached its maximum depth the hammer 61, 63 is retrieved from the conductor casing 1.

In the alternative embodiment where the outer pipe 5 has a stabilizer 71, this is driven into the unconsolidated sediments together with the outer pipe 5, the central pipe 73 of the stabilizer 71 abutting the stabilizer stop 27. The large surface area of the jacket 77 ensures, in a manner that is known per se, an increase in the lateral stability of the conductor casing 1 when placed in unstable unconsolidated sediments 51.

The conical shape of the locking member 9 ensures that the outer pipe 5 will not slip down the inner pipe 3 under stress, as the internal lip 43 of the locking member 9 will seize against the surface of the inner pipe 3.

The conductor casing 1 according the invention can assume a wide range of dimensions, as the inner pipe can assume all relevant dimensions according to industrial practice. 

1. A conductor casing device for establishing and lining a wellbore in unconsolidated sediments, the conductor casing being arranged to be driven into and to displace the unconsolidated sediments by axially directed impulses against an internal abutment in the lower portion of the conductor casing, wherein the conductor casing is telescopic.
 2. A device in accordance with claim 1, wherein an outer pipe is releasably coupled to an inner pipe by means of a coupling device.
 3. A device in accordance with claim 1, wherein an upper portion of the outer pipe is releasably coupled to an upper portion of the inner pipe.
 4. A device in accordance with claim 1, wherein one or more locking members abutting the outside wall of the inner pipe are arranged in a non-displaceable manner in the lower portion of the outer pipe.
 5. A device in accordance with claim 1, wherein the locking member(s) is/are arranged to allow an inner pipe released from the outer pipe to move axially away from the upper portion of the outer pipe.
 6. A device in accordance with claim 1, wherein that the locking member(s) is/are arranged to prevent an outer pipe released from the inner pipe to move axially towards the lower portion of the inner pipe.
 7. A device in accordance with claim 1, wherein the outer pipe is arranged to receive one or more externally placed stabilizers.
 8. A device in accordance with claim 7, wherein the outer pipe is provided with one or more stops arranged to abut an upper portion of the stabilizer(s).
 9. A device in accordance with claim 1, wherein the lower portion of the inner pipe is provided with a driving shoe arranged to receive axially directed driving impulses.
 10. A method of driving a conductor casing into unconsolidated sediments in order to establish and line a wellbore, the conductor casing being arranged to be driven into and to displace the unconsolidated sediments through axially directed impulses against an internal abutment in the lower portion of the conductor casing, wherein: an outer pipe is releasably coupled to the upper portion of an inner pipe; the assembled telescopic conductor casing is driven into the unconsolidated sediments until the upper portion of the outer pipe assumes a prescribed height above the surface of the unconsolidated sediments; the outer pipe is released from the inner pipe; the inner pipe is driven further into the unconsolidated sediments until it stops against a preferably impenetrable structure, the inner pipe moving axially away from the upper portion of the outer pipe.
 11. A method in accordance with claim 10, wherein one or more stabilizers are mounted on the outer pipe prior to driving this into the unconsolidated sediments. 